Australia’s Great Barrier Reef is the largest coral reef system in the world and the only living structure visible from space. Although ecosystem managers in Australia have worked hard to preserve the reefs, the past couple of decades have brought a new threat that can’t be solved by any one country alone: human-induced global warming.

Rising ocean temperatures have caused mass coral bleaching in coral reefs around the world, in every tropical ocean from the Caribbean to the South Pacific. This is now considered to be the biggest threat that coral reefs face, and they face many, including overfishing, pollution, storm damage, and invasive species.

The 2,300 kilometer (1,400 mile) long wonder of the natural world—home to 2,900 individual reefs, 1,500 species of fish, and 900 islands—has had obituaries written for it multiple times over the last few years. But the Great Barrier Reef is not dead.

Vox’s Joss Fong explains how coral reefs work, why they’re valuable, what’s happening when corals bleach, how the reefs could still recover, and what people would need to do to help that happen.

To see more of the GBR, watch this 2011 Undersea Productions promo vid:

Related vids: Incredible macro video of fluorescing corals & sponges and The seafloor microscope that can reveal corals’ secrets.

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